Cancer drug proves to be effective against multiple tumours

Cancer drug proves to be effective against multiple tumours

The 86 cancer patients were a disparate group, with tumours of the pancreas, prostate, uterus or bone. One woman had a cancer so rare that there were no tested treatments. She was told to get her affairs in order. Still, these patients had a few things in common. All had advanced disease that had resisted every standard treatment. All carried genetic mutations that disrupted the ability of cells to fix damaged DNA.

And all were enrolled in a trial of a drug that helps the immune system attack tumours. The results, published recently in the journal Science, are so striking that the Food and Drug Administration already has approved the drug, pembrolizumab for patients whose cancers arise from the same genetic abnormality.

It is the first time a drug has been approved for use against tumours that share a certain genetic profile, whatever their location in the body is. Tens of thousands of cancer patients each year could benefit. “This is absolutely brilliant,” said Dr José Baselga, physician in chief at Memorial Sloan Kettering Cancer Centre in New York, USA, which has just hired the study’s lead investigator, Dr Luis A Diaz Jr. After taking pembrolizumab, 66 patients had their tumours shrink substantially and stabilise, instead of continuing to grow. Among them were 18 patients whose tumours vanished and have not returned. There was no control group, which meant the results had to be absolutely compelling to be convincing.

The study started in 2013 and is funded by philanthropies; the drugmaker’s only role was to supply the drug. The study is continuing. The drug, made by Merck, is already on the market for select patients with a few types of advanced lung, melanoma and bladder tumours. It is
expensive, costing $156,000 a year. A test for the mutations targeted by the drug is already available, too, for $300 to $600. Just four percent of cancer patients have the type of genetic aberration susceptible to pembrolizumab.

Clinicians have long been accustomed to classifying cancers by their location in the body — patients are diagnosed with lung cancer, for example, or brain cancer. Yet researchers have been saying for years that what matters was the genetic mutation causing the tumours. At first, they were certain that they would be able to cure cancers with drugs that zeroed in on the mutations, wherever the tumours were lodged.

But cancers were more complicated than that, said Dr Drew M Pardoll, director of the Johns Hopkins Bloomberg-Kimmel Institute and an author of the new paper. A mutation that appeared in half of all melanomas, for example, turned out to be rare in other cancers. And even when scientists pinpointed that mutation in 10% of colon cancers, the drug that worked for melanoma patients did not work for other cancer patients.

The new study was based on a different idea. The immune system can recognise cancer cells as foreign and destroy them. But tumours deflect the attack by shielding proteins on their surface, making them invisible to the immune system. Pembroluzimab is a new type of immunotherapy drug known as a PD-1 blocker, which unmasks the cancer cells so that the immune system can find and destroy them. The drug is the happy result of a failed trial. A nearly identical drug, nivolumab, was given to 33 colon cancer patients, and just one showed any response — but his cancer vanished altogether.

What was special about that one patient? Luis, a geneticist at Johns Hopkins until now, and lead author of the new study, found the answer: a genetic mutation that prevented the tumour from repairing DNA damage. As a result, the man’s cancer cells contained a plethora of mutated genes, which produced thousands of strange-looking proteins on the surfaces of the cells. Once the tumour’s cloaking mechanism was short-circuited by the drug, the man’s immune system had no trouble targeting the foreign proteins on the cancer cells.

That led to the idea for Luis’s new study. He and his colleagues sought patients whose tumours had the same genetic defect, which can arise in any of four genes in a pathway that repairs damaged DNA. They gave these patients a PD-1 blocker and were surprised by the results. The drug’s effects have been so durable that the investigators do not know how long the results should be expected to persist or how long these patients might expect to survive. That kind of result, Baselga said, “is insane.”

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